The overall objective is to develop hepatitis C virus (HCV)-specific immunogens that may be useful as vaccines for the prevention of chronic HCV infection. In the first approach (Specific Aim 1), an HCV vaccine using a particulate carrier platform to deliver envelope-derived hypervariable region 1 (HVR1) consensus neutralizing epitopes will be developed. Modified woodchuck hepatitis core (WHcAg) particles will be used as a vaccine platform for several reasons: hybrid-WHcAg particles elicit extremely high levels of anti-insert antibodies; use of the WHcAg will not compromise the use of the anti-HBc diagnostic assay because the WHcAg and human hepatitis core antigen (HBcAg) are not crossreactive at the antibody level; the immune tolerance to HBcAg in HBV chronic carriers can be circumvented by the use of the WHcAg platform because the HBcAg and WHcAg are only partially crossreactive at the T cell level; a "WHcAg combinatorial technology" more versatile than the HBcAg in terms of accommodating the insertion of a greater variety of foreign epitopes has been recently developed. We propose to insert into the WHcAg platform consensus neutralizing sequences derived from the variable HVR1 region of E2 in order to address the problem of genetic variability of HCV. An important advantage of the WHcAg platform is that it is comprised of 240 subunits that self-assemble into particles. Therefore, multiple HVR1 consensus peptides can theoretically be inserted into the same WHcAg-HVR1 hybrid particle. In the second approach (Specific Aim 2) an HCV vaccine using the same WHcAg carrier platform to deliver E1-E2 conserved neutralizing epitopes will be designed and developed. An important problem in developing a prophylactic vaccine against HCV is the high genetic variability of the virus. In addition to multiple HVR1 consensus epitopes, an alternative approach is to identify epitopes or antigenic regions which are genetically stable or conserved. Therefore, highly or semi-conserved (across genotypes) neutralizing epitopes identified within the E1 or E2 domains, which may be poorly immunogenic during natural infection, will be inserted onto the WHcAg platform. The efficacy of these HVR1 consensus and conserved E1/E2-WHcAg hybrid particles will be analyzed for immunogenicity and characterized by testing the ability of the anti-HVR1 and anti-E1/E2 antisera generated by immunization to neutralize HCV pseudoparticle infection. Finally (Specific Aim 3) we propose to insert into the WHcAg platform a domain in NS3 containing CD4 and CD8 epitopes to broaden the efficiency of the immune response against HCV. This "T cell rich" domain of NS3 will be fused to the C-terminal of the hybrid-WHcAg platform. To efficiently induce a CTL response, we propose to use the equivalent of a prime-boost strategy. The immune system will be first primed by a DNA vaccine encoding the HCV-WHcAg-CD4+/CD8+ platform also containing neutralizing B cell sites, then we will boost with the homologous HCV-WHcAg-CD4+/CD8+ particulate protein. [unreadable] [unreadable] [unreadable]